Method and system for determining longest inappropriate water taking of estuary reservoir

Abstract

The invention discloses a method and a system for determining longest unsuitable water taking of an estuary reservoir, which are used for determining the longest unsuitable water taking days of the estuary reservoir based on a three-dimensional numerical model. The advanced three-dimensional numerical model is utilized to accurately simulate and predict saline intrusion. Meanwhile, by inputting specific hydrological conditions and dynamic factors, the method can calculate the longest continuous unsuitable water taking days of the estuary reservoir under the ultra-dry runoff condition, and important theoretical basis and technical support are provided for reservoir capacity design and dispatching of the reservoir.

Description

Technical Field

[0001] The present invention relates to the field of water conservancy projects, and particularly to a method and system for determining the longest inappropriable water intake days of an estuary reservoir. Background Art

[0002] With the acceleration of the urbanization process and the growth of the population, the demand for water resources is increasing day by day. As an important water source area, the rational development and utilization of water resources in the estuary area is particularly important. For example, multiple reservoirs have been built in the Yangtze River estuary area, providing a large amount of raw water for big cities such as Shanghai. However, the problem of saltwater intrusion faced by estuary reservoirs has become a key factor affecting the feasibility of water intake. According to the drinking water standard, the raw water cannot be used after the chloride concentration exceeds 250 mg / L, and the corresponding salinity is about 0.45. The intrusion of seawater into the estuary makes it impossible to obtain fresh water with low salinity around the reservoir. How long the reservoir can't obtain fresh water at most is a key factor in the reservoir capacity design. How to accurately determine the longest inappropriable water intake days of an estuary reservoir has important guiding significance for the reservoir capacity design and scheduling.

[0003] At present, the determination of the longest inappropriable water intake days of an estuary reservoir mainly relies on experience and simple two-dimensional numerical simulations, lacking systematicness and accuracy. Because the salinity stratification in the estuary area is obvious, the two-dimensional model is difficult to depict the vertical saltwater distribution and cannot reflect the actual saltwater intrusion situation, so the longest inappropriable water intake days of the estuary reservoir cannot be accurately determined.

[0004] Therefore, how to improve the systematicness and accuracy of the determination model for the longest inappropriable water intake days of an estuary reservoir is a problem to be solved in this field. Summary of the Invention

[0005] Regarding the technical problem that the determination model for the longest inappropriable water intake days of an estuary reservoir has low systematicness and accuracy, the purpose of the present invention is to provide a method for determining the longest inappropriable water intake of an estuary reservoir. This solution comprehensively considers various factors such as tides, runoff, wind stress, mixing, and river regime to solve the problems of lack of systematicness and accuracy in the prior art and the neglect of other important influencing factors. On this basis, a system capable of implementing the method for determining the longest inappropriable water intake of an estuary reservoir is also provided.

[0006] To achieve the above purpose, the present invention provides a method for determining the longest inappropriable water intake of an estuary reservoir, and the method for determining the longest inappropriable water intake of an estuary reservoir includes the following steps:

[0007] S1: Collection of data in the estuary reservoir area

[0008] This step is used to collect data on the shoreline and terrain of the selected estuary reservoir area;

[0009] S2: Define the conditions for the continuous non-withdrawal time

[0010] Based on the shoreline and terrain data of the estuary reservoir area selected in S1, calculate the continuous non-withdrawal time according to the drinking water standard;

[0011] S3: Establish a model

[0012] Based on the structure of the estuary reservoir area collected in S1 above, establish a three-dimensional numerical model;

[0013] S4: Model verification

[0014] Verify by comparing the collected observed data with the simulation results calculated by the model;

[0015] S5: Calculate the longest continuous non-withdrawal time

[0016] Based on the simulation results calculated by the model in S4, determine the longest continuous non-withdrawal time;

[0017] S6: Analyze the results and guide the reservoir design

[0018] This step is used to analyze the numerical values calculated in S5 above and guide the reservoir design according to the analysis results.

[0019] Furthermore, the establishment of the three-dimensional numerical model in S3 includes the following steps:

[0020] S31: Construct the control equations

[0021] The control equations include the momentum equation, the continuity equation, the temperature and salinity transport and diffusion equations, and the state equation, which jointly describe the changes of water flow, temperature and salinity in three-dimensional space;

[0022] S32: Set the initial conditions

[0023] Set the initial values of the flow velocity and water level with faster response time to zero;

[0024] S33: Determine the boundary conditions

[0025] The boundary conditions include the sea surface boundary condition, the seabed boundary condition, the solid boundary condition and the open boundary condition: the sea surface boundary condition, the seabed boundary condition, the solid boundary condition and the open boundary condition.

[0026] Furthermore, the sea surface boundary condition jointly describes the physical state of the sea surface through the flow velocity boundary condition and the dynamic boundary condition.

[0027] Furthermore, the seabed boundary condition also describes the physical state of the seabed through the flow velocity boundary condition and the dynamic boundary condition.

[0028] Furthermore, the model validation in S4 includes the following steps:

[0029] S41: Collect the observed data related to the model simulation area;

[0030] S42: Preprocess the collected observed data to ensure the accuracy and integrity of the observed data;

[0031] S43: Configure the initial conditions, boundary conditions, and physical parameters of the model according to the observed data and the actual situation;

[0032] S44: Input the above-configured parameters into the model constructed in S3 for operation to generate simulation results, and the simulation results should include the variable time series data corresponding to the observed data;

[0033] S45: Compare and verify the simulation results with the collected observed data;

[0034] S46: Conduct problem diagnosis and optimization based on the comparison results.

[0035] Furthermore, the comparison and verification in S45 include:

[0036] Time series comparison: Compare the simulation results with the observed data collected in S41 in terms of time series and analyze the differences between the two;

[0037] Statistical index evaluation: Quantitatively evaluate the simulation results using statistical indices;

[0038] Spatial distribution comparison: Compare the spatial distribution of the simulation results with the observed data collected in S41 and analyze the spatial consistency between the two.

[0039] Furthermore, the problem diagnosis and optimization in S46 include:

[0040] Identify problems: Identify the problems existing in the model according to the results of the comparison and verification in S44;

[0041] Optimize the model: Make corresponding adjustments and optimizations to the model for the identified problems;

[0042] Repeat verification: Conduct repeated verification on the optimized model.

[0043] Furthermore, the calculation of the longest continuous non-withdrawable water time in S5 includes the following steps:

[0044] S51: Extract salinity data: Extract the salinity time series data of the reservoir water intake from the simulation results calculated in S4;

[0045] S52: Set a threshold: Set a salinity threshold according to the water quality standard and water intake requirements;

[0046] S53: Calculate the continuous unsuitable water intake time: Traverse the salinity time series data, find the time periods that continuously exceed the threshold, and record the start and end times, as well as the duration, of each continuous unsuitable water intake time period.

[0047] S54: Determine the longest continuous unsuitable water intake time: Compare the durations of all continuous unsuitable water intake time periods, and find the maximum value among them. This maximum value is the longest continuous unsuitable water intake time.

[0048] Furthermore, the reservoir design takes into account the impact of the longest continuous unsuitable water intake time on the reservoir capacity.

[0049] To achieve the above object, the present invention provides a system for determining the longest unsuitable water intake in an estuary reservoir. The system for determining the longest unsuitable water intake in the estuary reservoir includes:

[0050] A collection module, which is used to collect data on the shoreline and terrain of the estuary reservoir area.

[0051] A definition module, which interacts with the collection module in terms of data. Based on the selected estuary reservoir area, it calculates the continuous unsuitable water intake time according to the drinking water standard.

[0052] A model establishment module, which interacts with the collection module and the definition module in terms of data. Based on the data of the estuary reservoir area collected and the determined continuous unsuitable water intake time, it constructs a three-dimensional numerical model of the estuary reservoir.

[0053] A model verification module, which interacts with the model establishment module in terms of data and is used to verify the constructed three-dimensional numerical model.

[0054] A calculation module, which interacts with the model verification module in terms of data. Through the verified three-dimensional numerical model, it calculates the longest continuous unsuitable water intake time.

[0055] An analysis module, which interacts with the calculation module in terms of data and is used to analyze the values calculated by the calculation module and guide the reservoir design according to the analysis results.

[0056] The method and system for determining the longest unsuitable water intake in the estuary reservoir provided by the present invention realizes the determination of the longest unsuitable water intake days in the estuary reservoir based on a three-dimensional numerical model. This method comprehensively considers various factors such as tides, runoff, wind stress, mixing, and river regime, and uses an advanced three-dimensional numerical model to accurately simulate and predict saltwater intrusion.

[0057] At the same time, by inputting specific hydrological conditions and dynamic factors, this method can calculate the longest consecutive number of days when estuary reservoirs are not suitable for water extraction under extremely low-flow conditions, providing an important theoretical basis and technical support for the reservoir capacity design and scheduling. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0059] Figure 1 This is a flow chart of the method for determining the longest number of days when water is not suitable for the estuary reservoir;

[0060] Figure 2 This is an example diagram of the location of Bantansha;

[0061] Figure 3 This is an example diagram of runoff after diversion and drainage along the Yangtze River below Datong;

[0062] Figure 4 This is an example diagram of the calculation range of the model;

[0063] Figure 5 An example diagram for the computational verification of the model;

[0064] Figure 6 An example graph showing the temporal changes of water level, surface salinity at the upstream output point and surface salinity at the downstream output point of the Xiabiantansha waters calculated by the model. DETAILED DESCRIPTION

[0065] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further explained below with reference to specific diagrams.

[0066] The present invention aims to solve the technical problem that the model for determining the longest number of days that estuary reservoirs are not suitable for water extraction is not systematic and accurate, and proposes a method for determining the longest number of days that estuary reservoirs are not suitable for water extraction based on a three-dimensional numerical model. The method comprehensively considers multiple factors such as tides, runoff, wind stress, mixing and river flow, and uses advanced three-dimensional numerical models to accurately simulate and predict saltwater intrusion. By inputting specific hydrological conditions and dynamic factors, the method can calculate the longest continuous number of days that estuary reservoirs are not suitable for water extraction under extremely low runoff conditions, providing an important theoretical basis and technical support for the storage capacity design and scheduling of reservoirs.

[0067] The method for determining the longest number of days when water is not suitable for estuary reservoirs provided by the present invention is as follows: Figure 1 , including the following steps:

[0068] S1: Data collection in estuary reservoir area

[0069] This step is used to collect data on the shoreline and topography of the selected estuary reservoir area.

[0070] S2: Define the conditions for the continuous non - water - taking time

[0071] Based on the shoreline and terrain data of the estuary reservoir area selected in Step 1, this step calculates the continuous non - water - taking time according to the drinking water standard.

[0072] S3: Establish a model

[0073] Based on the structure of the estuary reservoir area collected in S1 above, this step establishes a three - dimensional numerical model. The specific steps for model establishment are as follows:

[0074] S31: Construct the control equations

[0075] The control equations include momentum equations, continuity equations, temperature and salinity transport - diffusion equations, state equations, etc. These equations jointly describe the changes of water flow, temperature, and salinity in three - dimensional space.

[0076] Among them, the momentum equation is used to describe the motion state of water flow in three - dimensional space, and its formula is as follows:

[0077]

[0078] The continuity equation is used to describe the continuity of water flow, that is, water flow is incompressible and mass - conserved, and its formula is as follows:

[0079]

[0080] The temperature and salinity transport - diffusion equations are used to describe the transport and diffusion processes of temperature and salinity in water flow, and their formula is as follows:

[0081]

[0082] The state equation is used to describe the relationship between the density, temperature, and salinity of water, and its formula is as follows:

[0083] ρ total = ρ total (θ, s) (6)

[0084] In the above - mentioned control equations:

[0085]

[0086] Among them, D is the total water depth, ζ is the sea - surface fluctuation, x, y, and z are the eastward, northward, and upward directions of the Cartesian coordinate axes respectively, and the vertical coordinate It varies from the seabed at -1 (z = -h) to the sea surface at 0 (z = ζ). u1 and v1 are the velocity components in the directions of the horizontal non-orthogonal curves ξ(x,y) and η(x,y) respectively, u and v are the velocity components in the x and y directions, J is the Jacobian function, h1 and h2 are the factors after transforming the orthogonal grid into a non-orthogonal grid, θ and s are the temperature and salinity respectively, f and g are the Coriolis parameter and the acceleration due to gravity respectively, Km and Kh are the vertical eddy viscosity coefficient and the vertical eddy diffusivity coefficient respectively, ρ is the perturbation density, and ρ o is the reference density, and the sum of the two is the total density ρ total . Fξ, Fη, Fθ and Fs represent the horizontal diffusion terms of momentum (in the ξ and η directions), temperature and salinity respectively, as follows:

[0087]

[0088] where Am is the horizontal viscosity coefficient, Ah is the horizontal diffusion coefficient, which is generally equal to Am. A is a constant, taking 0.02. The vertical viscosity coefficient Km and the vertical diffusion coefficient Kh.

[0089] S32: Set the initial conditions

[0090] The initial values of the flow velocity and water level (u, v, w, ζ) with a relatively fast response time are set to zero. The adjustment of the ocean thermal process models such as temperature and salinity is relatively slow, and generally, measured data or multi-year average climatological data are taken according to the actual situation:

[0091] θ(ξ, η, σ, 0) = θ * (ξ, η, σ) (11)

[0092] s(ξ, η, σ, 0) = s * (ξ, η, ) (12)

[0093] S33: Determine the boundary conditions

[0094] When constructing a three-dimensional numerical model of an estuarine reservoir, the boundary conditions are the key to model solving. They define the values or variation laws of physical quantities (such as flow velocity, temperature, salinity, etc.) on the external boundaries of the model calculation area. The selection and setting of boundary conditions directly affect the accuracy and applicability of the model. By setting reasonable boundary conditions, more realistic distributions of water flow, temperature and salinity can be simulated, thus improving the prediction ability of the model.

[0095] S331: Sea surface boundary conditions: It jointly describes the physical state of the sea surface through the flow velocity boundary conditions and the dynamic boundary conditions

[0096] The flow velocity boundary conditions specify the flow velocity distribution on the sea surface, and its equation is as follows:

[0097]

[0098] The dynamic boundary condition considers the influence of wind stress on the sea surface:

[0099] The wind stress vector The components in the ξ and η directions are τsξ and τsη respectively, and the equations are as follows:

[0100]

[0101] where ρ a is the air density, is the wind speed at 10 m above the sea surface, and is the sea surface drag coefficient. The drag coefficient CD is given by the formula of Large and Pond (1981).

[0102] S332: Seabed boundary condition: It also describes the physical state of the seabed through the velocity boundary condition and the dynamic boundary condition.

[0103] The velocity boundary condition stipulates the velocity distribution on the seabed, and its equation is as follows:

[0104]

[0105] The dynamic boundary condition considers the influence of bottom friction stress on the seabed:

[0106] The bottom friction stress vector The components in the ξ and η directions are τbξ and τbη respectively, as follows:

[0107]

[0108] where u1b and v1b are the components of the bottom layer velocity in the ξ and η directions respectively, Cd is the bottom drag coefficient, and in the deeper river channels outside the north branch, the following relationship is satisfied:

[0109]

[0110] where к is the von Kármán constant, z0 is the seabed roughness, and zab represents the distance from the bottom layer velocity point to the seabed boundary.

[0111] For the north branch area, due to the extremely shallow water depth, the above formula for solving Cd using the logarithmic law is not applicable, and it can be solved by the Manning formula in which the Manning roughness coefficient varies with water depth.

[0112] The above sea surface and seabed boundary conditions are interrelated through physical quantities such as water flow, temperature, and salinity. They jointly determine the distribution and variation laws of water flow, temperature, and salinity in the estuarine reservoir.

[0113] S333: Solid boundary (shore boundary) condition

[0114] At the solid boundary, the following conditions are usually satisfied:

[0115] v t = 0 (23)

[0116] v n = 0 (24)

[0117]

[0118] Where t and n represent the tangential and normal directions of the solid boundary respectively.

[0119] S334: Open boundary (water boundary) conditions

[0120] For the open boundary conditions, items such as water level, flow velocity, temperature, salinity, etc. can be given according to the measured data or according to the radiation boundary conditions.

[0121] S4: Model verification

[0122] This step is used to verify the three-dimensional numerical model constructed in step 3 above. The verification process includes the following steps:

[0123] S41: Collect observation data: Collect the observation data related to the model simulation area, including the time series data of variables such as water flow velocity, direction, temperature, salinity, etc. These data should come from reliable observation sources, such as hydrological stations, ocean observation stations, etc.

[0124] S42: Process the observation data: Preprocess the collected observation data, including data cleaning, filling in missing values, dealing with outliers, etc. Ensure the accuracy and integrity of the observation data.

[0125] S43: Configure model parameters: According to the observation data and the actual situation, configure the initial conditions, boundary conditions, physical parameters, etc. of the model. These parameters should be as close to the real situation as possible to ensure the accuracy of the model.

[0126] S44: Input the above-configured parameters into the model constructed in S3 for operation to generate simulation results. The simulation results should include the time series data of variables corresponding to the observation data.

[0127] S45: Comparative verification

[0128] Time series comparison: Compare the simulation results with the observation data collected in S41 in terms of time series, and analyze the differences between the two. Through the comparison, the prediction ability of the model in the time series can be evaluated.

[0129] Statistical index evaluation: Quantitatively evaluate the simulation results using statistical indices (such as root mean square error, correlation coefficient, Nash efficiency coefficient, etc.). These indices can reflect the accuracy and reliability of the model simulation.

[0130] Spatial distribution comparison: Compare the spatial distribution of the simulation results with the observed data collected in S41, and analyze the spatial consistency between the two. Through this comparison, the prediction ability of the model in terms of spatial distribution can be evaluated.

[0131] S46: Problem diagnosis and optimization

[0132] Identify problems: Based on the results of the comparison and verification in S44, identify the problems existing in the model. These problems may include unreasonable parameter settings, model structure defects, etc.

[0133] Optimize the model: For the identified problems, make corresponding adjustments and optimizations to the model. For example, adjust model parameters, improve the model structure, etc.

[0134] Repeat verification: Conduct repeated verification on the optimized model to ensure that the accuracy and reliability of the model are improved.

[0135] S5: Calculate the longest continuous unsuitable water intake time

[0136] S51: Extract salinity data: Extract the continuous salinity change data from the simulation results calculated in S4, especially the salinity time series data at the reservoir water intake, with at least one data point per hour.

[0137] S52: Set the threshold: According to the water quality standard and water intake requirements, set a salinity threshold, for example, it can be 0.45. When the salinity exceeds this threshold, the water quality is considered unsuitable for water intake.

[0138] S53: Calculate the continuous unsuitable water intake time: Traverse the salinity time series data to find the time periods that continuously exceed the threshold (continuously exceeding the threshold for more than 4 hours, and less than or equal to 4 hours is not counted as the non - water - intake time). These time periods are the continuous unsuitable water intake times. Record the start and end times, as well as the duration, of each continuous unsuitable water intake time period.

[0139] S54: Determine the longest continuous unsuitable water intake time: Compare the durations of all continuous unsuitable water intake time periods and find the maximum value. This maximum value is the longest continuous unsuitable water intake time.

[0140] S6: Analyze the results and guide the reservoir design

[0141] This step is used to analyze the values calculated in step 5 above and guide the reservoir design based on the analysis results.

[0142] Consider the impact of the longest continuous non-withdrawable time on the reservoir capacity. If the longest continuous non-withdrawable time is long, it may be necessary to increase the reservoir capacity to ensure that the constructed reservoir reserves sufficient water resources.

[0143] For the method for determining the longest non-withdrawable days of the estuary reservoir given in the present example solution, in specific applications, a corresponding software program can be formed to create a system for determining the longest non-withdrawable days of the estuary reservoir. When this software program runs, it will execute the above-mentioned method for determining the longest non-withdrawable days of the estuary reservoir, and at the same time, it will be stored in a corresponding storage medium for the processor to retrieve and execute.

[0144] The system for determining the longest non-withdrawable days of the estuary reservoir thus formed mainly includes, in terms of function: a collection module, a definition module, a model establishment module, a model verification module, a calculation module, and an analysis module.

[0145] The collection module in this system is used to collect data on the shoreline and terrain of the estuary reservoir area.

[0146] This data collection module is configured to execute the above steps for collecting data on the estuary reservoir area to achieve the corresponding functions.

[0147] The definition module in this system interacts with the collection module in terms of data. Based on the selected estuary reservoir area, and in accordance with the drinking water standard, it calculates the continuous non-withdrawable time.

[0148] This definition module is configured to execute the above steps for defining the conditions for the continuous non-withdrawable time to achieve the corresponding functions.

[0149] The model establishment module in this system interacts with the collection module and the definition module in terms of data. Based on the data of the estuary reservoir area collected and the determined continuous non-withdrawable time, it constructs a three-dimensional numerical model of the estuary reservoir.

[0150] This model establishment module is configured to execute the above steps for establishing the model to achieve the corresponding functions.

[0151] The model verification module in this system interacts with the model establishment module in terms of data and is used to verify the constructed three-dimensional numerical model.

[0152] This model verification module is configured to execute the above steps for model verification to achieve the corresponding functions.

[0153] The calculation module in this system interacts with the model verification module in terms of data and calculates the longest continuous non-withdrawable time through the verified three-dimensional numerical model.

[0154] This calculation module is configured to execute the above steps for calculating the longest continuous non-withdrawable time to achieve the corresponding functions.

[0155] The analysis module in this system interacts with the calculation module, which is used to analyze the values calculated by the calculation module and guide the reservoir design according to the analysis results.

[0156] The analysis module is configured to execute the above steps of the analysis results and guide the reservoir design to implement the corresponding functions.

[0157] The following is an example to illustrate its working process in specific applications. It should be noted that the following working process is only for example and does not limit this solution.

[0158] Step 1: Select the extremely dry hydrological year

[0159] According to the "Code for Urban Water Supply Engineering Planning" (GB50282-98), the guaranteed rate of low-flow of urban water supply sources can be 90-97%. Considering that Shanghai is an international metropolis, the guaranteed rate of low-flow is taken as ≥97%. The design of the Qingcaosha Reservoir uses the statistical frequency of the low-season runoff (from November to March) of the Datong Station on the Yangtze River with a relatively long series as the guaranteed rate of low-flow. According to the analysis, the dry season from 1978 to 1979 is a typical extremely dry year, and the corresponding frequency is about 98%. In this example, this year is used as the calculation hydrological year for the time when water intake is not suitable in the Biandansha waters, and the correction of the Three Gorges Dam and the water intake and drainage along the river to the runoff into the sea is considered. The daily variation diagram of the measured and modified Yangtze River runoff at Datong from September 20, 1978 to May 31, 1979 is as Figure 2 , from January 1 to March 15, 1979, the runoff at Datong varies between 6500-8000 m3 / s, maintaining a particularly low runoff for a long time.

[0160] Step 2: Define the continuous unsuitable water intake time

[0161] According to the drinking water standard, when the chloride content of raw water exceeds 250 mg / L, it cannot be drunk, and the corresponding salinity is about 0.45. If the continuous water intake time is less than 4 hours, it is still regarded as unsuitable for water intake; the duration of salinity exceeding the drinking water standard plus the duration of continuous water intake time less than 4 hours is the continuous unsuitable water intake time. The longest continuous unsuitable water intake time refers to the maximum value of the continuous unsuitable water intake time of the reservoir, which is an important parameter required for the reservoir capacity design.

[0162] Step 3: Build and verify the three-dimensional model

[0163] Calculation range: The calculation range of this model includes the Yangtze River Estuary, Hangzhou Bay and adjacent sea areas ( Figure 3 ). The west boundary is located at the low-tide limit Datong of the Yangtze River Estuary, near about 117.5° east longitude. The open boundary in the open sea is located near 125° east longitude on the east side, near 33.5° north latitude on the north side, and near 27.5° north latitude on the south side.

[0164] Grid division: Horizontally, the model has a grid distribution of 337×225 grids. Vertically, σ-coordinates are adopted and evenly divided into 10 layers. The grid resolution can reach about 100 m at the bifurcation of the north and south branches, about 200 m in the lower section of the north branch, and has a high resolution inside the estuary mouth to ensure high resolution. The grids outside the estuary are relatively sparse, with a maximum resolution of about 10 km, to balance the computational efficiency and accuracy.

[0165] Governing equations

[0166] The model is based on the governing equations of the ECOM-si model, including momentum equations, continuity equation, temperature and salinity transport-diffusion equations, and equation of state. These equations describe the motion laws and variation characteristics of water flow, temperature, and salinity in three-dimensional space.

[0167] The momentum equations consider the effects of factors such as gravity, pressure, friction, and Coriolis force on water flow; the continuity equation ensures the continuity of water flow; the temperature and salinity transport-diffusion equations describe the transport and diffusion processes of temperature and salinity in water flow; and the equation of state provides a formula for calculating water density.

[0168] The model uses advanced numerical methods to solve the governing equations, such as the finite difference method or the finite volume method.

[0169] Initial conditions and boundary conditions

[0170] Initial conditions: The initial values of flow velocity and water level with a fast response time are set to zero, while physical quantities with slower changes such as temperature and salinity are set according to measured data or multi-year average climate data.

[0171] Boundary conditions:

[0172] Sea surface boundary conditions: Include flow velocity boundary conditions and dynamic boundary conditions, where the dynamic boundary conditions consider the influence of wind stress on the sea surface.

[0173] Seabed boundary conditions: Include flow velocity boundary conditions and dynamic boundary conditions, where the dynamic boundary conditions consider the influence of bottom friction stress on the seabed.

[0174] Solid boundary (shore boundary) conditions: Satisfy the no-slip condition, that is, the flow velocity is zero at the solid boundary.

[0175] Open boundary conditions: The open boundary in the open sea is driven by tidal level and residual water level. The tidal level considers 16 tidal components (M2, S2, N2, K2, K1, O1, P1, Q1, MU2, NU2, T2, L2, 2N2, J1, M1, and OO1), which are synthesized from the harmonic constants of each tidal component.

[0176] The upstream open boundary is given in the form of flux, using the measured runoff data of Datong Hydrological Station. For the wind field, the Weather Research Forecast Model (WRF model) is used in the model validation, or the numerical product with a time resolution of 6 hours and a spatial resolution of 0.125°×0.125° provided by ECMWF (European Centre for Medium-Range Weather Forecasts) is used.

[0177] According to the observed data and actual conditions, the initial conditions, boundary conditions, physical parameters, etc. of the model are configured. These parameters should be as close to the actual situation as possible to ensure the accuracy of the model. The above configured parameters are put into the model constructed in S3 for operation to generate simulation results.

[0178] Then, the generated simulation results were verified by selecting the flow velocity, direction and salinity measured data near the reservoir, and the results showed that the calculation results were accurate. Figure 4 As shown in the figure, the simulation results and the observed data show a high degree of consistency in both time series and spatial distribution, verifying the accuracy and reliability of the model. This provides a strong scientific basis and decision-making support for subsequent reservoir design and water resources management.

[0179] Step 4: Calculation of the longest continuous time when water is not suitable for extraction

[0180] The three-dimensional numerical model constructed in step 3 is used to calculate the daily data of the modification of runoff by the Three Gorges Reservoir and the diversion and drainage along the river, as well as dynamic factors such as tides, stress and mixing. The model starts calculation on September 1, 1978 and ends on May 3, 1979.

[0181] Figure 5 The water level and surface salinity of the upstream output point R1 and the surface salinity of the downstream output point R2 in the Xiabiantansha waters calculated by the model change with time. It can be seen that the salinity has a significant half-monthly change with the water level. During the extremely dry runoff period from January to March 1979, the salinity peak increased. The highest salinity occurred in early February, with the maximum values ​​of points R1 and R2 reaching 2.35 and 2.25 respectively. With the change of large and small tides, the salinity has a half-monthly period of salinity trough. At point R1, the salinity is lower than 0.45 every half month, resulting in the longest continuous time that is not suitable for water extraction less than 15 days; at the R2 output point, the salinity trough in mid-February is close to but greater than 0.45, resulting in the longest continuous time that is not suitable for water extraction far greater than 15.

[0182] After carefully checking the salinity data file of the model output points, the number of consecutive days when water intake is not advisable for each section can be given. At the upstream point R1, from mid-December 1978 to early April 1979, the periods when consecutive water intake is not advisable are respectively from 19:20 on December 16, 1978 to 03:10 on December 26, 1978, with a duration of 8.33 days; from 13:10 on December 30, 1978 to 05:50 on January 10, 1979, with a duration of 10.69 days; from 12:30 on January 12 to 18:30 on January 25, with a duration of 13.25 days; from 01:20 on January 28 to 20:20 on February 10, with a duration of 13.79 days; from 00:30 on February 11 to 02:50 on February 23, with a duration of 12.10 days; from 12:40 on February 26 to 03:50 on March 9, with a duration of 10.63 days; from 01:30 on March 13 to 00:40 on March 22, with a duration of 8.83 days; from 06:40 on March 29 to 11:50 on April 3, with a duration of 4.73 days. Among them, the longest consecutive period when water intake is not advisable is 13.79 days.

[0183] At the downstream point R2, from mid-December 1978 to early April 1979, the periods when consecutive water intake is not advisable are respectively from 07:00 on December 17, 1978 to 17:40 on December 26, 1978, with a duration of 9.44 days; from 21:10 on December 30, 1978 to 05:20 on January 11, 1979, with a duration of 11.38 days; from 01:00 on January 13 to 05:40 on January 27, with a duration of 14.19 days; from 00:30 on January 28 to 04:00 on February 24, with a duration of 26.15 days; from 12:00 on February 26 to 04:50 on March 10, with a duration of 11.70 days; from 00:40 on March 13 to 23:10 on March 22, with a duration of 9.94 days; from 07:10 on March 29 to 23:50 on April 3, with a duration of 5.69 days. Among them, the longest consecutive period when water intake is not advisable is 26.15 days.

[0184] In the south branch of the Yangtze River Estuary, if only affected by the saltwater intrusion from the north branch, the salinity in the upstream is higher than that in the downstream. For example, the saltwater intrusion into the Dongfengxisha Reservoir is greater than that into the Chenhang Reservoir; if mainly affected by the frontal saltwater intrusion from the downstream, the salinity in the downstream is higher than that in the upstream, such as the areas of the sandbars at the entrance of the North Channel, the North Passage and the South Passage. Although the spatial distance between the model output points R1 and R2 in the Xiabiandansha water area is not far, the longest consecutive period when water intake is not advisable at the upstream R1 point, which is 13.79 days, is much shorter than that at the downstream R2 point, which is 26.15 days, with a difference of 12.36 days. This indicates that under extremely low runoff, the influence of the frontal saltwater intrusion from the downstream on the R2 point is much greater than that on the R1 point.

[0185] In summary, at the current stage, when simulating and predicting the saltwater intrusion in estuary reservoirs, the traditional two-dimensional numerical simulation method is mainly used, which has the disadvantages of being difficult to accurately depict the vertical saltwater distribution, lacking systematicness and accuracy, and ignoring other important influencing factors. The present invention designs an advanced three-dimensional numerical model, comprehensively considers various factors such as tides, runoff, wind stress, mixing, and river regime, and accurately determines the longest consecutive days during which water intake in the estuary reservoir is not advisable in the face of saltwater intrusion.

[0186] When the prior art determines the longest days during which water intake in the estuary reservoir is not advisable, it lacks accurate and reliable simulation and prediction results and is difficult to guide the reasonable design and effective scheduling of the reservoir. The present invention, however, designs an advanced three-dimensional numerical model, comprehensively considers various factors, and accurately determines the longest consecutive days during which water intake in the estuary reservoir is not advisable in the face of saltwater intrusion. Compared with the prior art, the present invention provides more accurate and reliable simulation and prediction results, can guide the reasonable design and effective scheduling of the reservoir, and ensures that the reservoir capacity design and scheduling can meet the drinking water safety requirements.

[0187] In summary, the present invention has significant advantages in simulating and predicting the saltwater intrusion in estuary reservoirs and can provide a scientific basis for reservoir management and scheduling.

[0188] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and the descriptions in the specification only illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. A method for determining the longest period of time when water is not suitable for taking from an estuary reservoir, characterized in that: The method for determining the longest period of time when the estuary reservoir is not suitable for water withdrawal comprises the following steps: S1: Data collection in estuary reservoir area This step is used to collect data on the shoreline and topography of the selected estuary reservoir area; S2: Clarify the definition of continuous water withdrawal time This step is based on the shoreline and topographic data of the estuary reservoir area selected by S1, and according to the drinking water standard, calculates the continuous time when water is not suitable for extraction; S3: Building the Model This step is to establish a three-dimensional numerical model based on the structure of the estuary reservoir area collected in S1 above; S4: Model Validation This step is verified by collecting observation data and comparing them with the simulation results calculated by the model; S5: Calculate the longest continuous time when water is not suitable for extraction This step determines the longest continuous time when water extraction is not suitable based on the simulation results calculated by the model in S4; S6: Analyze results and guide reservoir design This step is used to analyze the value calculated by S5 above and provide guidance for reservoir design based on the analysis results.

2. The method for determining the longest period of time when water is not suitable for taking water from an estuary reservoir according to claim 1, characterized in that: The establishment of the three-dimensional numerical model in S3 includes the following steps: S31: Constructing the governing equations The governing equations include momentum equation, continuity equation, temperature and salinity transport and diffusion equation, and state equation, which together describe the changes of water flow, temperature and salinity in three-dimensional space; S32: Setting initial conditions Set the initial values ​​of flow rate and water level with faster response time to zero; S33: Determine boundary conditions Boundary conditions include sea surface boundary conditions, seabed boundary conditions, solid boundary conditions and open boundary conditions: sea surface boundary conditions, seabed boundary conditions, solid boundary conditions and open boundary conditions.

3. The method for determining the longest period of time when water is not suitable for taking water from an estuary reservoir according to claim 2, characterized in that: The sea surface boundary conditions describe the physical state of the sea surface through velocity boundary conditions and dynamic boundary conditions.

4. The method for determining the longest period of time when water is not suitable for taking water from an estuary reservoir according to claim 2, characterized in that: The seabed boundary conditions also describe the physical state of the seabed through velocity boundary conditions and dynamic boundary conditions.

5. The method for determining the longest period of time when water is not suitable for taking water from an estuary reservoir according to claim 1, characterized in that: Model validation in S4 includes the following steps: S41: Collect observational data related to the model simulation area; S42: pre-processing the collected observation data to ensure the accuracy and completeness of the observation data; S43: Configure the initial conditions, boundary conditions and physical parameters of the model according to the observed data and actual conditions; S44: Put the above configured parameters into the model constructed in S3 to run and generate simulation results. The simulation results should include variable time series data corresponding to the observed data; S45: Compare and verify the simulation results with the collected observation data; S46: Perform problem diagnosis and optimization based on the comparison results.

6. The method for determining the longest period of time when water is not suitable for taking water from an estuary reservoir according to claim 5, characterized in that: The comparative verification in S45 includes: Time series comparison: compare the simulation results with the observation data collected in S41 in time series and analyze the differences between the two; Statistical indicator evaluation: Use statistical indicators to quantitatively evaluate simulation results; Spatial distribution comparison: Compare the spatial distribution of the simulation results with the observation data collected in S41 to analyze the spatial consistency between the two.

7. The method for determining the longest period of time when water is not suitable for taking water from an estuary reservoir according to claim 5, characterized in that: Problem diagnosis and optimization in S46 include: Identify problems: Based on the results of the comparison and verification in S44, identify the problems in the model; Optimize the model: adjust and optimize the model accordingly based on the identified problems; Repeated validation: Repeated validation of the optimized model.

8. The method for determining the longest period of time when water is not suitable for taking water from an estuary reservoir according to claim 1, characterized in that: The calculation of the longest continuous unsuitable water extraction time in S5 includes the following steps: S51: extract salinity data: extract salinity time series data of the reservoir water intake from the simulation results calculated in S4; S52: Setting threshold: Setting a salinity threshold according to water quality standards and water intake requirements; S53: Calculate the continuous time when water extraction is not suitable: traverse the salinity time series data, find the time period that continuously exceeds the threshold, and record the start and end time of each continuous time period when water extraction is not suitable, as well as the duration; S54: Determine the longest continuous time when water is not suitable for extraction: compare the duration of all continuous time periods when water is not suitable for extraction, and find out the maximum value therein, which is the longest continuous time when water is not suitable for extraction.

9. The method for determining the longest period of time when water is not suitable for taking from an estuary reservoir according to claim 1, characterized in that: The reservoir design takes into account the impact of the longest continuous period of unsuitable water withdrawal on the reservoir capacity.

10. A system for determining the longest period of time when water is not suitable for taking from an estuary reservoir, characterized in that: The system for determining the longest period of time when the estuary reservoir is not suitable for water withdrawal includes: A collection module, the collection module is used to collect data on the shoreline and topography of the estuary reservoir area; A definition module, wherein the definition module interacts with the data of the collection module, and calculates the continuous time when water is not suitable for extraction based on the selected estuary reservoir area and according to the drinking water standard; A model building module, wherein the model building module interacts with the data of the collection module and the definition module, and constructs a three-dimensional numerical model of the estuary reservoir based on the collected estuary reservoir area data and the clear continuous unsuitable water extraction time; A model verification module, which interacts with the model building module to verify the constructed three-dimensional numerical model; A calculation module, wherein the calculation module interacts with the model verification module to calculate the longest continuous time when water is not suitable for extraction through the verified three-dimensional numerical model; The analysis module interacts with the calculation module data to analyze the values ​​calculated by the calculation module and provide guidance for reservoir design based on the analysis results.

Images